The present invention relates to a radiation detecting device and its manufacturing method, and more specifically to a radiation detecting device suited for combined use with a medical X-ray CT scanner and a method of manufacturing it.
The currently available radiation detecting device used in medical X-ray CT scanners comprises a scintillator--in place of the conventional Xe ionization chamber type detector--that converts incident radiations into light and a photoelectric converter that converts the light from the scintillator into electric signals. These components are securely bonded together by a transparent bonding agent. This detector is generally called a radiation solid-state detector, known for its high S/N ratio (signal to noise ratio).
In more concrete terms, on the surface of a semiconductor substrate on which arrayed photodiodes (photoelectric converters) are formed, scintillators isolated from each other by isolation plates for each corresponding photodiode are arranged via the bonding agent.
With a radiation detecting device of such configuration, however, uniformity of output from each diode is lost because of variations in the scintillator layout orientation with respect to the semiconductor substrate and in the thickness of the transparent bonding agent layer interposed between the scintillator and the semiconductor substrate.
In other words, the linear characteristic of the scintillator (characteristic of sensitivity for a change in the radiation energy spectrum) varies depending on the angle of incidence of the incoming radiation. This characteristic is more pronounced in a polycrystalline sinter scintillator (hereinafter referred to as ceramic scintillator) than in a monocrystalline scintillator.
The bonding agent has not only the function of fixing the scintillators to the semiconductor substrate but also the function of facilitating the introduction of the light produced by the scintillators toward the photodiodes. This requires that both the layout orientation of the scintillators with respect to individual photodiodes and the optical characteristic of the bonding agent be uniform.
The fluid characteristic of the bonding agent, however, makes it difficult for the bonding agent layer to be uniform over the entire area when the scintillators are bonded to the semiconductor substrate by the bonding agent. This in turn causes variations in optical characteristic of the bonding agent corresponding to each photodiode.